Knife-sharpening machine

ABSTRACT

The invention relates to a knife sharpening machine comprising a plate-type holding device on which two intersecting sharpening bars are rotationally mounted and loaded in relation to each other by means of springs. The sharpening bars, at least in the grinding area, are made of a ceramic material. The plate is provided with a slit which is open on one end and closed on the other, extending as far as the intersection point of the sharpening bars. When pressure is exerted by the knife in the direction of the closed slit end, the sharpening bars are spread apart from each other counter to the force of the springs. Curved guides are provided on both sides of the slit. The ends of the sharpening bars, facing away from the axes of rotation thereof, are guided therein.

This invention relates to a knife sharpening apparatus having a holdingdevice on which two intersecting sharpening rods are pivotally mountedand loaded toward each other by springs, the holding device having aslot open at the end facing away from the rotation axes of thesharpening rods and closed at the end facing the rotation axes of thesharpening rods, said slot extending to the intersection point of thesharpening rods so that upon pressure of the knife on the intersectingsharpening rods in the direction of the closed end of the slot thesharpening rods are spread apart against the force of the springs.

Such an apparatus is known from U.S. Pat. No. 5,478,272. The sharpeningrods are made of steel. The springs swiveling the sharpening rods towardeach other are constituted by coil springs acting on the rotation axesof the sharpening rods. The grinding power of the known apparatus leavessomething to be desired. Also, the known apparatus is difficult to cleansince when unclean knives are sharpened liquid debris can pass into thearea of the rotation axes with the coil springs.

The problem of the invention is to decisively improve the knownapparatus in terms of grinding power and hygiene.

This is obtained according to the invention by the measures stated inclaim 1.

Sharpening rods are thus used according to the invention that are madeof ceramics at least in the grinding area. This achieves high grindingpower. Ceramic materials to be used are in particular oxides, carbides,borides, nitrides or silicides of metals or of the nonmetals with eachother, for example silicon carbide, or metal oxides, metal carbides,metal borides, metal nitrides or metal silicides in particular oftungsten, titanium, niobium or tantalum, for example tungsten carbide.Such metal compounds are also referred to as hard metals. Since ceramicrods withstand only little bending stress, the sharpening rods areguided according to the invention at the ends facing away from theirrotation axes in guides formed in an arc shape with a radiuscorresponding to the length of the rods.

To shorten the grinding time due to a long grinding surface, the twosharpening rods preferably have according to the invention a rectangularcross section at least in the grinding area, the opposing sides of thetwo rectangles extending parallel to each other. Thus the knife touchesthe full width of the two sharpening rods during grinding. That is, at awidth of the sharpening rods of for example 0.5 to 1 centimeter theknife is in contact with the sharpening rods over a length of 1 to 2centimeters during grinding.

The ceramic material in the grinding area can also be formed by aninsert in the sharpening rods.

Sharpening of knives causes material to be removed substantially evenlyover the length of the sharpening rods. However, this does not apply tothe portion of the sharpening rods at the closed end area of the slot.Here, a step forms in the ceramic rods in the course of time, which canlead to the knife becoming blunt instead of sharp during grinding.

To remedy this, the two sharpening rods preferably have according to theinvention on the opposing sides a portion tapering toward the rotationaxis of the rod in the closed end area of the slot. Said taperingportions can be formed for example by constrictions of the sharpeningrods in this area.

The sharpening rods are preferably each fastened to a pin pivotallymounted on the holding device.

The springs swiveling the sharpening rods toward each other can beformed by torsion bars extending on each side of the slot and fastenedat one end rotationally fast to the pin and at the other end on the sameside of the slot to the holding device. The springs are thus readilyaccessible from outside and easy to clean. The torsion bars can beformed for example by a leaf spring or spring wire.

The holding device is preferably constituted by a plate, the curvedguides for the sharpening rods being constituted by curved slots in theplate. For guidance in the curved guides of the plate, the sharpeningrods each have at the end facing away from the rotation axis a pin onwhich a portion with reduced diameter is provided for engaging therelevant guide slot.

The pins for pivotally mounting the sharpening rods can likewise have aportion with reduced diameter for engaging a bore in the plate. The pinsfor pivotally mounting the rods and/or the pins for guiding the rods arepreferably made of plastic and are provided with receiving means inwhich the ends of the rods are inserted. The ceramic rods inserted intothe plastic pins are thus soft mounted. The receiving means have a crosssection corresponding to the sharpening rods, thus being likewiserectangular if the rods have a rectangular cross section.

On the other side of the plate there is a counterpart connectable withthe particular pin and having a larger diameter than the portion withreduced diameter. For connecting the counterpart with the pin, a plugconnection or snap connection can be provided for example. However, theconnection is preferably formed by a screw connection. This can be sodesigned e.g. that the counterpart is formed as a screw that is screwedinto an internal thread provided in the portion of the pin with reduceddiameter. Conversely, the counterpart can be formed as a nut that isscrewed onto a screw thread provided on the portion of the pin withreduced diameter.

All four pins and all four counterparts for mounting and guiding therods can be of identical form, whereby, since the rods are offset fromthe holding device or holding plate, the distance of the receiving meansfrom the plate is smaller in the case of the two pins receiving the rodoffset from the plate than in the case of the two other pins.

On the outside of the rods facing away from the grinding surface, aplate-shaped finger guard is mounted on each rod to prevent one's handfrom coming in contact with the knife if the holding device is held withthe hand during grinding.

In the following, an embodiment of the inventive knife grindingapparatus will be explained in more detail by way of example withreference to the drawing, in which:

FIG. 1 and FIG. 2 show front and side views of the inventive apparatus;

FIG. 3 shows a section along line III—III in FIG. 2; and

FIG. 4 shows a section through a pin adapted to be slipped onto one endof a sharpening rod for mounting or guiding the rod, with a counterpart.

According to FIGS. 1 and 2, the apparatus has holding plate 3 fastenedwith screws 2 on plate-shaped pedestal 1.

Holding plate 3 has pivotally mounted thereon two intersectingsharpening rods 4, 5 with axes 6, 7 extending perpendicular to plate 3.In the middle, holding plate 3 has vertical slot 8 that is open at upperend 9 bell mouthed upward, and closed at lower end 10. Lower end 10 islocated above two rotation axes 6, 7 located on one and the other sideof the perpendicular to slot 8.

So that sharpening rods 4, 5 can intersect, they are offset from plate3. That is, rod 5 is disposed closer to plate 3 than rod 4. Rods 4, 5extending parallel to holding plate 3 are made of ceramics, for examplesilicon carbide. At the upper end facing away from rotation axes 6, 7,rods 4, 5 are guided in holding plate 3 in curved slots 12, 13 extendingon one and the other side of slot 8.

Rods 4, 5 are fastened to pins 14, 15 pivotally mounted on holding plate3. The ends of rods 4, 5 are loaded toward each other in accordance witharrows 16, 17 by torsion bars 18, 19 extending on either side of slot 8and fastened at one end rotationally fast to pin 14, 15 and at the otherend bent and inserted into corresponding bores in plate 3.

Slot 8 serving to receive and guide a knife with blade 21 to besharpened extends to intersection point 20 of spread-apart rods 4, 5.That is, the pressure of the knife or blade 21 in the direction ofclosed end 10 of the slot spreads apart rods 4, 5 against the force ofsprings 18, 19, as shown in FIG. 1.

As to be seen in FIG. 3, ceramic rods 4, 5 have a square or rectangularcross section, whereby opposing sides a, b of the two rectangles extendparallel to each other. A triangular cross section is also possible,however, in which case the opposing sides of the two triangles extendparallel, or, in general, the two opposing sides of the two polygons ifrods 4, 5 have a polygonal cross section.

Rods 4, 5 are worn out by sharpening knives in the course of time. Astep can thereby develop in lower end area 10 of slot 8 in the course oftime. To prevent the formation of such steps, rods 4, 5 have a taperingform in this area, due to constrictions 23, 24.

For guidance in curved slots 12, 13, rods 4, 5 each have at the upperend pin 25, 26 provided with portion 27 with reduced diameter forengaging guide slot 12, 13. In the same way, pins 14, 15 each have onrotation axis 6, 7 a portion with reduced diameter for engaging bore 31,32 in holding plate 3. Pins 14, 15 and 25, 26 are made of plastic. Sincepins 14, 15 and 25, 26 are of identical form, only pin 14 is shown inFIG. 4. Pin 14 is provided with rectangular pocket-like receiving means33, 34 in which one end of rod 4, 5 is inserted. Fine blind bore 35 ofpin 14 receives the end of torsion bar 18, 19. Through bores 37, 38moisture can escape from receiving means 33, 34. Portion 27 with reduceddiameter has internal thread 40 in which cap screw 42 is screwed as acounterpart. Unused receiving means 33 or 34 can be closed.

In upper area 9 of slot 8, plate 3 has lateral gaps 41, 42.

According to FIG. 1, rods 4, 5 each have on the outside curved plate 44,45, shown by dashed lines, as a finger guard for example made ofplastic, said plates extending parallel to holding plate 3 and beingaxially offset. Further, inserts 46, 47 shown by dashed lines in FIG. 1are provided in the grinding area of rods 4, 5 and made of ceramics. Ifsuch ceramic inserts 46, 47 are used, constrictions 23, 24 can beomitted. Apart from inserts 46, 47, rods 4, 5 can then be made ofplastic for example. Also, it is then possible to form rods 4, 5integrally with finger-guard plates 44, 45.

1. A knife sharpening apparatus having a holding device on which twointersecting sharpening rods are pivotally mounted and loaded towardeach other by springs, said holding device having a slot open at one endand closed at the other end and extending to an intersection point ofthe sharpening rods so that upon pressure of a knife in the slot in thedirection of the closed end of the slot the sharpening rods are spreadapart against the force of the springs, wherein the sharpening rods aremade of ceramics at least in a grinding area, and curved guides areprovided on each side of the slot for guiding ends of the sharpeningrods facing away from their rotation axes.
 2. A knife sharpening deviceaccording to claim 1, wherein the two sharpening rods have a polygonalcross section, opposing sides of the two polygons extending parallel toeach other.
 3. A knife sharpening device according to claim 1, whereinthe two sharpening rods have on opposing sides a portion tapering towardthe rotation axes in a closed end area of the slot.
 4. A knifesharpening device according to claim 1, wherein the ceramics consists ofsilicon carbide or tungsten carbide.
 5. A knife sharpening deviceaccording to claim 1, wherein the holding device is fastened to a base.6. A knife sharpening device according to claim 1, wherein thesharpening rods are each fastened to a respective pin pivotally mountedon the holding device.
 7. A knife sharpening device according to claim6, wherein the springs swiveling the sharpening rods toward each otherare formed by torsion bars extending on either side of the slot andfastened at one end rotationally fast to the respective pin and at theother end to the holding device.
 8. A knife sharpening apparatusaccording to claim 6, wherein the pins for pivotally mounting thesharpening rods and a second pair of pins for guiding the sharpeningrods are formed of plastic and have receiving means for insertion of theends of the sharpening rods.
 9. A knife sharpening device according toclaim 1, wherein the holding device is formed by a plate and the curvedguides constitute curved guide slots in the plate.
 10. A knifesharpening device according to claim 9, wherein each said sharpening rodis provided for guidance in the respective curved guide slot at the endfacing away from the respective rotation axis with a second pin having aportion with reduced diameter for engaging the guide slot.
 11. A knifesharpening apparatus according to claim 9, wherein the pins forpivotally mounting the sharpening rods have a portion with reduceddiameter for engaging a respective bore in the plate.
 12. A knifesharpening apparatus according to claim 11, wherein a counterpartconnectable with the pins and having a larger diameter than the portionwith reduced diameter is provided on the other side of the plate.
 13. Aknife sharpening apparatus according to claim 9, wherein a base to whichthe holding plate is fastened is formed by a pedestal.
 14. A knifesharpening apparatus according to claim 1, wherein the slot is bellmouthed in an open end area.